FIG. 1 is a circuit diagram of a conventional LED light source module 10. As shown in the FIG. 1, the conventional LED light source module 10 includes a plurality of light-emitting units 11 each connected to a direct-current (DC) voltage source 12 in parallel. Each of the light-emitting units 11 includes a resistor 111 and a plurality of LEDs 112, wherein the LEDs 112 and the resistor 111 are connected in series so that the LEDs 112 can be powered on by the DC voltage from the DC voltage source 12 and emit light.
Referring to FIG. 1, in case of stable voltage from the DC voltage source 12, the magnitude of current entering the LEDs 112 in each light-emitting unit 11 is constant under the control of the resistor 111 series-connected to the LEDs 112, so the LEDs 112 emit light steadily.
However, a slight fluctuation in the voltage from the DC voltage source 12 will result in significant variation in the current entering the light-emitting units 11. The unstable current not only has a destabilizing effect on the luminance of light emitted by the LEDs 112 in the light-emitting units 11, but also causes the LEDs 112 to generate heat unsteadily, which may in turn shorten the service lives of the LEDs 112.